1. Field of the Invention
The present invention relates to a device for recovering the vapors leaving a fuel tank of a motor vehicle driven by an internal combustion engine and, more particularly, to such a device designed to allow its leaktightness to be tested.
Current motor vehicles are commonly equipped with devices capable of providing the fuel vapors generated in the tank from being released into the atmosphere, in order to limit the pollution thereof with hydrocarbons. For this purpose, a filter cartridge is used which is connected to the fuel tank in which the hydrocarbons contained in the vapors leaving the fuel tank are separated from the air by one or more layers of active charcoal. In order to prevent saturation of this filter cartridge, it is regenerated using periodic flushing with atmospheric air sucked into the cartridge through an atmospheric connection orifice under the effect of a partial vacuum applied to a third orifice connected to the intake manifold of the internal combustion engine via a purge control solenoid valve.
Certain regulations, and in particular those of the Californian Air Rescue Board (CARB) stipulate that the operation of such a device .shall be capable of being tested in order for a deficiency such as, for example, a leaktightness defect of the device, to be signaled to the driver of the vehicle.
2. Description of the Related Art
A device is known from the prior art, for example from French Patent 2,635,823, for recovering the fuel vapors, which device consists of a fuel tank, a filter cartridge connected by a first duct to said tank and by a second duct to a purge solenoid valve connecting the cartridge with the partial vacuum which prevails in the intake manifold of the engine, in which the absence leaks in the circuit is diagnosed by measuring the partial vacuum which is set up in the tank during a purge phase. From German Patent DE 40-03-751, such a device is also known in which the filter cartridge is fitted, on its atmospheric connection orifice, with a blocking solenoid valve making it possible to isolate the device from the surrounding air in order to diagnose even smaller leaks. However, such devices have the drawback, during a leaktightness test of the circuit, of introducing into the intake manifold of the engine a mixture of fuel vapors which can seriously disturb the operation of devices for controlling the richness of the air/fuel mixture supplied to the engine. In fact, the introduction of vapors heavily loaded with fuel, as is the case when the cartridge is close to saturation, increases the fuel richness of the mixture introduced into the combustion chamber and then leads either to an excess pollution or, in the case of feed systems in closed loop with respect to the richness of the mixture, to a significant reduction in the quantity of fuel injected. In this case, at the end of the test, removal of this addition of vapors leads to a mixture which is too lean in fuel, which may cause combustion misfires and engine knocking which are prejudicial to driving.
The object of the present invention is therefore to provide a device for recovering fuel vapors which makes it possible to carry out a leaktightness test of the device, without having the drawbacks of the prior art.